More than ever, companies have to cope with ever changing market conditions. Some companies have reacted to shortened product life cycles, constant changes in customer preferences and cost pressures by implementing mass customization practices. Mass customization has been hailed as a way to overcome the tradeoff between cost and flexibility performance. However, there is lack of consistent empirical evidence to demonstrate that this really is the case. We advance this debate by proposing that in order for mass customization to be more effective, a company needs to possess and utilize social capital (i.e., cognitive, relational and structured social capital) within their supply networks. This study uses primary survey data from 513 plants from nine countries collected by the Global Manufacturing Research Group (GMRG). We used structural equation modelling analysis to test our hypotheses. Results indicate that mass customization has the ability to improve a company’s cost and flexibility performance. Furthermore, results regarding the moderating role of social capital are mixed. Cognitive capital only moderates the impact of mass customization on cost performance while relational capital increases this impact on both cost and flexibility performance. Structural capital does not moderate the impact of mass customization on performance